1. Field of the Invention
This invention relates in general to pre-cast concrete and steel composite structural members, such as used in modular bridge structures, and more particularly, to modular composite structural members which use a pre-compression assembly for the joint during construction, refurbishing and/or widening.
2. Description of the Prior Art
Large structures, such as bridges are well known and are obviously time-consuming to build or widen and even more time-consuming to rehabilitate. Typically, a bridge structure will have longitudinally extending girders with a concrete deck surface. The concrete deck is made composite with the girders by pouring the concrete in place around shear connectors connected to the girders. The structure may be formed upside down and then inverted to place it in its final operating position. This latter specialized technique is disclosed in U.S. Pat. Nos. 4,493,177, 4,646,493, 4,700,516, 5,144,710, 5,301,483, 5,305,575 and 5,553,439, copies of which are incorporated herein by reference.
To form such composite members of the type having an upper concrete surface and a metal support underneath, a mold typically is utilized. First, the steel supports, such as girders or beams, are placed beneath a mold assembly having two or more mold pieces disposed around and supported by the supports. Next, the concrete is poured into the mold such that the concrete fills the mold and extends over the girders or beams. When the concrete is hardened, the mold pieces are disassembled from around the supports such that the concrete rests on the supports. In most instances, these types of structural members are formed in place. This is usually advantageous so the concrete deck surface can better fit into the finished structure. The concrete deck portion is attached to the beams by shear connectors which are molded into the concrete, or which extend into openings in the concrete, which are then grouted in place. This technique works satisfactorily in many cases, particularly in original bridge construction where the area of construction is readily accessible.
When separate prefabricated composite units are used, the sections are positioned adjacent to one another, and the metal support members in those sections, such as girders or beams, are then positioned on the piers or abutments. This technique is particularly useful when it is not feasible to form the entire structure in place or when the use of prefabricated members can save construction time on site. It also works well in bridge widening projects where prefabricated members are installed next to the existing structure.
Certain construction constraints, such as those in which a bridge structure is being repaired or otherwise refurbished or rehabilitated, make many prior art methods of construction more expensive and result in associated problems, such as traffic delays. In repair or refurbishing, typically the old concrete deck, or at least a part of it, is removed, and another deck must be put in its place. If the replacement deck must be poured in place, molds must be set up, the concrete poured, and then the concrete allowed time to cure before a bridge structure can be reopened to traffic. In high-density traffic areas, this creates considerable traffic tie-up problems, which result in significant lost time and inconvenience to commuters and other travelers.
The use of prefabricated composite units which can be set in place, such as those described above, greatly reduces the repair time involved. That is, the old structure may be removed, and the new structure simply set in place on the piers or abutments and attached to them. Because of the prefabrication, the time necessary to construct molds, pour concrete and allow the concrete to cure all can occur prior to the placement of the composite units. Thus, thexe2x80x9cdown timexe2x80x9d to repair the bridge structure is greatly reduced, which lowers costs and pleases motorists. However, this technique creates longitudinal and transverse joints that need to be filled and which become potential pathways for water and salt-laden water to fall objectionably on other parts of the structure.
The present invention all but eliminates this objectionable leakage without adding construction time to a constrained time window, such as occurs in overnight construction, because the modular units can carry traffic before they are permanently clamped together. In the present invention, prefabricated composite units are still positioned adjacent to one another, but are also pulled and clamped together by a pre-compression assembly which holds all of the units together in place. The structure can make use of match-casting the abutting faces so the usual xc2xe to xc2xd inch wide gap is narrowed. The joint may be filled with an adhesive applied to the abutting faces of the joint before they are pulled together. Whether used with match-cast, abutting faces or a conventional, hardened, grout-filled joint, pre-compressing the joint has the advantage of creating an extremely water-tight joint and, at the same time, supplementing the tensile resistance of the joint adhesive with pre-compressive stresses. In the event that tensile stresses are produced in the joint that exceed the pre-compression combined with the tensile strength of the joint adhesive, the size of the formed crack is limited to less than about 0.001 inches by the pre-stressed steel immediately beneath the joint.
One conventional approach to pre-compressing bridge structures is to install conduit in the deck portions thereof which is accomplished by positioning the conduit and pouring the moldable material around it. Steel cables are installed in these conduits after the bridge structure is erected and compression applied to the structure in a transverse direction by post-tensioning the steel cables. This process has several problems, one of which is the difficulty of aligning the conduits during the erection of the bridge structure. Further, there is a potential for damaging both the cable and its protective coating when the cable is pulled through misaligned conduits. Additionally, any such damage and consequent future deterioration is not visible which can lead to unexpected and sudden failure. In the present invention, any future deterioration of the pre-compression components is readily visible and much more easily corrected than with hidden and buried cable.
The present invention is a composite structural member, such as used in bridge construction. The member generally comprises a plurality of composite units, each unit itself comprising a plurality of longitudinally extending girders or floor beams disposed on bridge supports and a deck portion made of a moldable material and attached to the beams. The member further comprises pre-compression means for clamping adjacent units together such that a gap between the facing deck portions thereof is substantially closed and a joint formed therebetween is pre-compressed. The joint may be filled with a hardened high-strength grout.
In one preferred embodiment, one of the first and second transversely facing sides of at least one of the deck portions of the units defines a groove therein, and the other of the first and second transversely facing sides of at least one of the deck portions has a tongue portion thereon adapted for extending into the groove of an adjacent, facing deck portion such that upper surfaces of the adjacent deck portions are held substantially aligned and positioned coplanar. An adhesive may be disposed in the gap between the deck portions and in the groove.
Facing beams of adjacent units define holes therein which are substantially aligned, and the pre-compression means comprises a threaded member disposed through the holes on the facing beams and fastener means threadingly attached to the threaded member when tightened on the threaded member. In one embodiment, the threaded member is a bolt extending through one of the holes in one of the facing beams and one of the holes in the other of the facing beams, and the fastening means is characterized by a nut attached to the bolt.
A diaphragm connection plate is preferably attached to facing beams of adjacent units, and a diaphragm is attached to the adjacent diaphragm connection plates after the pre-compression means has been actuated to close the gap between the deck portions of the adjacent units. The diaphragm connection plate extends substantially transversely so that it is substantially perpendicular to the beams. A stiffener plate may be attached to the beam substantially parallel to the diaphragm connection plate, and thus, the stiffener plate preferably extends substantially transversely. The pre-compression is preferably disposed between the diaphragm connection plate and the stiffener plate.
The composite units may be prefabricated in an inverted position prior to being positioned on the supports, although the invention is not intended to be limited to this type of construction.
In an alternate embodiment, the invention may be described as a structural member for use on a structural support adjacent to an existing structure in which the structural member comprises a composite unit, a clamping member, attaching means for attaching the clamping member to the existing structure, and pre-compression means for clamping the composite unit against the existing structure after the clamping member is attached thereto such that a gap between deck portions of the composite unit and the existing structure is substantially closed and the joint formed therebetween is pre-compressed in a direction substantially perpendicular to the beams. The joint may be grout-filled. The composite unit comprises a plurality of substantially parallel beams adapted for positioning on the structural support, and a deck support made of a moldable material attached to the beams.
In a situation where the existing structure includes similar composite units, the clamping member may be characterized by one of the beams of such composite units. In this case, the structure and assembly thereof are similar to that previously described.
However, when the existing structure does not lend itself to the previously described attachment, such as when the existing structure has a concrete girder, the clamping member may be characterized by an angled member attached to a lower surface of the deck portion-of the existing structure.
The clamping member preferably defines one or more holes therein which are aligned with holes in a facing beam of a composite unit. The pre-compression means comprises a threaded member disposed through the holes in said clamping member and said facing beam, and fastener means threadingly attached to the threaded member thereon for pulling the clamping member and facing beam toward one another when tightened on the threaded member.
The present invention also includes a method of repairing a bridge structure comprising the steps of (a) prefabricating a plurality of composite units, each composite unit comprising a plurality of substantially parallel beams and a deck portion made of a moldable material and attached to the beams, (b) removing an old deck portion and girder portion therebelow of the bridge from an area above the bridge supports, (c) positioning at least some of the composite units in the area to replace the old deck and girder portions such that the beams in the units extend substantially longitudinally and (d) clamping facing beams on adjacent units together in a transverse direction so that a gap defined between facing unit deck portions of the adjacent composite units is substantially closed.
Step (a) preferably comprises prefabricating the units such that an overall height thereof is no greater than a height of the old bridge portion. The method may further comprise, prior to step (d), positioning shims between the beams and supports such that upper surfaces of the unit deck portions are substantially coplanar with an upper surface of the old deck portion.
Step (a) may comprise prefabricating the units in an inverted position.
Step (a) may also comprise forming at least some of the unit deck portions such that the deck portion has a first transversely facing side defining a groove therein and a second transversely facing side having a tongue portion thereon adapted for extending into the groove of an adjacent unit deck portion after step (d) such that upper surfaces of the adjacent deck portions are substantially aligned and held coplanar. The method may further comprise, prior to step (d), placing an adhesive in the gap and/or in the groove so a substantially watertight seal is formed.
In the preferred embodiment, step (d) comprises positioning a threaded member through aligned holes in the facing beams of the adjacent units, attaching a fastener to the threaded member, and tightening the fastener on the threaded member and thereby pulling the facing beams toward one another. The threaded member may be a bolt, and the fastener may comprise a nut attached to the bolt.
The method may further comprise the steps of (e) attaching a transversely extending diaphragm-connection plate to each of the facing beams, and (f) attaching, after step (d) a diaphragm to adjacent diaphragm connection plates on the facing beams to connect the beams together. Step (e) may be part of step (a). The bolts and nuts may be subsequently removed. Alternatively, the diaphragm may be omitted and the bolts and nuts left in place, in which case the pre-compressed ends of the deck portions also function as a diaphragm. In this latter case, the diaphragm connection plate is preferably replaced with a stiffener plate.
The present invention also includes methods of widening a bridge structure. One of these is a method of widening a bridge having an existing beam thereon comprising the steps of (a) prefabricating a composite unit comprising a plurality of substantially parallel unit beams, and a unit deck portion made of a moldable material and attached to the unit beams, (b) positioning the unit adjacent to an old section of the bridge structure such that the unit beams extend longitudinally with respect to the bridge structure and one of the unit beams is a facing unit beam with respect to the existing beams, and (c) clamping the facing beam and existing beam together such that a joint formed between a side of the bridge structure and a facing unit deck portion is pre-compressed. Step (a) preferably comprises prefabricating the units in an inverted position.
This method of widening a bridge may further comprise, prior to step (c), placing a hardenable grout in the joint.
Step (c) comprises forming a plurality of holes in the existing beam corresponding to a plurality of holes defined in the facing beam, positioning a threaded member through aligned holes in the existing beam and the facing beam, attaching a fastener to the threaded member, and tightening the fastener on the threaded member such that the existing beam and facing beam are biased toward one another.
For widening a bridge structure which does not have an existing metal beam, the method may be described as one comprising the steps of (a) prefabricating a composite unit comprising a plurality of substantially parallel unit beams, and a unit deck portion made of a moldable material and attached to the unit beams, (b) positioning the unit adjacent to an old section of the bridge structure such that the unit beams extend longitudinally with respect to the bridge, (c) attaching a clamping member to a lower surface of the bridge adjacent to a side thereof, and (d) clamping the clamping member to a facing unit beam on the composite unit together such that a joint formed between the side of the bridge and a facing unit deck portion is pre-compressed. Step (a) preferably comprises prefabricating the units in an inverted position.
This other widening method may further comprise, prior to step (d), placing a hardenable grout in the joint.
Step (d) comprises positioning a threaded member through aligned holes in the facing beam and the clamping member, attaching a fastener to the threaded member, and tightening the fastener on the threaded member such that the facing beam and clamping member are biased toward one another.
The methods of widening may also comprise, prior to the step of pre-compressing, positioning shims between the beams and supports such that an upper surface of the unit deck portion is substantially coplanar with an upper surface of the old bridge section.
In the preferred embodiment of the member, the clamping member is attached to the lower surface of the deck portion of the old bridge section using a plurality of anchor bolt assemblies.
Numerous objects and advantages of the invention will become apparent as the following detailed description of the preferred embodiment is read in conjunction with the drawings illustrating such embodiment.